Thioetherification processes for the removal of mercaptans from gas streams

ABSTRACT

This invention relates to thioetherification processes for the removal of mercaptans in charge gas streams. In particular, the invention relates to thioetherification processes for the removal of mercaptans using a catalyst comprising palladium and silver.

FIELD OF THE INVENTION

The present invention relates to thioetherification processes for theremoval of mercaptans in charge gas streams. In one embodiment, theinvention relates to thioetherification processes for the removal ofmercaptans using a catalyst comprising palladium and silver.

BACKGROUND

Thermal cracking of petroleum-related materials produces a variety oforganic chemical components, including mercaptans. One of the productsof the thermal cracking process is a gaseous stream, typically referredto as a “charge gas stream”, containing various C₁ to C₆ hydrocarbons,hydrogen and CO₂. The hydrocarbon portion of the charge gas streamcontains a mixture of olefins, diolefins and acetylenic components. Thecharge gas stream also typically contains various sulfur containingbyproducts of the cracking process, including H₂S and variousmercaptans, such as methyl, ethyl, propyl and butyl mercaptans.

The charge gas stream resulting from thermal cracking may containconcentrations of up to 1000 ppm mercaptans. Mercaptans are known topoison or deactivate noble metal selective hydrogenation catalysts. Thepresence of mercaptans can reduce the effectiveness and life ofcatalytic hydrogenation reactors, essential parts of conventional chargegas purification and separation processes. Existing caustic scrubbertechnology of charge gas streams, effective for removal of H₂S and CO₂,is ineffective for the removal of mercaptans.

Most industrial processes can tolerate mercaptan concentrations of up to1000 ppm. Olefin selective hydrogenation systems are designated aseither “front-end” (upstream of hydrogen removal) or “back-end”(downstream of hydrogen removal). In conventional back-end or front-endethylene plants, the mercaptans are separated from the charge gas bydistillation before they reach the hydrogenation stage. In back-endsystems, due to the boiling point of mercaptans, the mercaptans arecontained within the C₅+ stream and therefore end up in the pygasstabilization section away from the hydrogenation catalyst. In the firststage of the pygas purification section, liquid phase hydrogenation isperformed using a high Pd (<0.4%) or a Ni-based sulphur tolerantcatalyst. In the second stage of the pygas purification process, gasphase hydrodesulphurization (HDS) is performed using Co—Mo or Ni—Mocatalysts specifically designed to reduce total sulphur to very lowlevels.

In one type of front-end system, where the overhead of a depropanizer isfed into a front-end hydrogenation reactor, only methyl-mercaptan islight enough to have an effect. Because the concentration ofmethyl-mercaptan is normally in the low ppm level at that point, it isexpected to have some effect, but this effect can be minimized by theuse of higher catalyst loading or higher operating temperatures. Therest of the mercaptans and other sulphur compounds are eliminated in thepygas stabilization section as previously described.

Some industrial processes cannot tolerate mercaptan concentrations of upto 1000 ppm. These processes, such as the front-end CD-Hydro and olefinmetathesis reactions, require very low levels of mercaptans in the feed.In the front-end CD-Hydro process, hydrogenation takes place togetherwith distillation before the heavier mercaptans have been removed. TheCD-Hydro catalyst, which is a noble metal catalyst, can therefore bedeactivated unless mercaptans have been removed from the feed. As aresult, it is preferred that mercaptan levels in the feed are atconcentrations less than 5 ppm. A traditional solution used commerciallyto remove oxygenates and sulphur compounds from hydrocarbon streams isan absorber guard bed made of a zeolite material. This is not a viablealternative for these processes because the high reactivity of thecharge gas feed will foul the bed, rapidly making it ineffective.

The olefin metathesis process also has very stringent requirements forthe mercaptan levels in the feed. Based on their boiling point, certainmercaptans, such as methyl and ethyl-mercaptan, are contained in the C₄olefin stream that feeds the metathesis reactor. Currently, an adsorberbed with a zeolite molecular sieve material is used to remove oxygenatesand sulphur compounds from this stream. However, mercaptans canpotentially lower the effectiveness of these guard beds to oxygenateremoval. Removing the mercaptan compounds upstream from this process inthe charge gas treatment area will reduce the absorbent volumerequirement and increase the effectiveness of this guard bed inoxygenate removal.

The extraction of mercaptans from hydrocarbon streams is widelypracticed in refining. One commercially known process, MEROX®, isdescribed in U.S. Pat. Nos. 2,988,500, 4,626,341 and 5,424,051, each ofwhich is hereby incorporated by reference in its entirety. MEROX®, aswell as the related Thiolex process, uses caustic regeneration and hasbeen used in fuel gases, cracked gasoline, LPG streams and heavierfractions. These streams are mostly liquid and have a relatively lowolefinic and diolefinic content (i.e., they are not very reactive).Charge gas, on the other hand, has a very high olefinic content with asignificant amount of diolefins and acetylenics making these scrubbingmethods ineffective.

Thioetherification has been used for the removal of mercaptans fromrefinery streams. For instance, U.S. Pat. No. 6,231,752 (the entirety ofwhich is hereby incorporated by reference), describes the removal ofmercaptans from a light naphtha stream as part of a CatalyticDistillation Hydrosulfurization process using a Ni-based catalyst. Thisprocess takes advantage of the thioetherification reaction for sulphurremoval via formation of heavy sulphur species components and theirremoval through the bottoms of the catalytic distillation column.However, the liquid phase reaction mechanism for this technology is onlyeffective for diolefins. In particular, butadiene and isoprene can reactwith mercaptans to produce thioethers such as butyl-ethyl or C₅-ethylsulfide. U.S. Pat. Nos. 6,849,773 and 6,919,016 (the entirety of each ofwhich is hereby incorporated by reference) describe the same process fora C₄ stream.

U.S. Pat. No. 5,851,383 (the entirety of which is hereby incorporated byreference) describes a diolefin hydrogenation-thioetherification processover a Ni-based catalyst on a C₃-C₅ FCC stream. A combination of a fixedbed hydrogenation reactor and a distillation column are disclosed forthe removal of heavy sulphur components. This system is a back endsystem in which hydrogen is fed as a separate stream, at a low level,with the C₃-C₅ stream in a fixed bed reactor. The feed stream used inthe system described in U.S. Pat. No. 5,851,383 is much lower inreactive species than charge gas.

As such, there exists an ongoing and unmet need in the industry forprocesses to remove mercaptans from charge gas streams.

SUMMARY OF THE INVENTION

The present invention relates to processes for removing mercaptans fromcharge gas streams. In one aspect, the invention relates to a processcomprising the steps of feeding a gas phase mixture comprising hydrogen,hydrocarbons and mercaptans, which is rich in reactive species such asdiolefins and acetylenics, to a reactor comprising a catalyst which iscapable of catalyzing the thioetherification of mercaptans to thioethersto produce a reactor product mixture; feeding the reactor productmixture to a distillation unit comprising an upper section and a lowersection which is capable of separating lower boiling point hydrocarbonsfrom the thioethers wherein the lower boiling point hydrocarbons aresubstantially contained in the upper section and the thioethers aresubstantially contained in the lower section; and recovering the lowerboiling point hydrocarbons from the upper section.

In another aspect, the invention relates to a process for removingmercaptans comprising the steps of feeding a gas phase comprisinghydrocarbons and mercaptans to a distillation unit comprising (i) afirst catalyst which is capable of catalyzing the thioetherification ofmercaptans to thioethers, (ii) a gas phase mixture feed point, and (iii)an upper section and a lower section. The distillation unit is capableof separating lower boiling point hydrocarbons from the thioethers. Thelower boiling point hydrocarbons are substantially contained in theupper section and the thioethers are substantially contained in thelower section. The feed point is positioned between the first catalystand the lower section and the lower boiling point hydrocarbons arerecovered from the upper section.

In yet another aspect, the present invention relates to a process forremoving mercaptans comprising the steps of feeding a liquefiedpetroleum gas mixture comprising hydrocarbons and mercaptans to areactor comprising a catalyst which is capable of catalyzing thethioetherification of mercaptans to thioethers to produce a reactorproduct mixture, wherein the reactor is supplemented with hydrogen gas;feeding the reactor product mixture to a distillation unit comprising anupper section and a lower section which is capable of separating lowerboiling point hydrocarbons from the thioethers, wherein the lowerboiling point hydrocarbons are substantially contained in the uppersection and the thioethers are substantially contained in the lowersection; and recovering the lower boiling point hydrocarbons from theupper section.

One advantage of the present invention is that mercaptans present incharge gas streams, including liquefied petroleum gas, at relativelyhigh levels, such as about 1000 ppm, are reduced to relatively lowerlevels, such as about less than 5 ppm. The mercaptan reductionessentially eliminates the poisoning effect of these mercaptans onsulphur sensitive processes and materials, such as the CD-Hydro catalystand metathesis catalyst, making both more efficient and economical.Another advantage of the present invention is the reduction of lightmercaptans, such as the reduction of methyl-mercaptan in front-endacetylene converter reactors when used between the front-enddepropanizer and the hydrogenation reactor. Light mercaptan reductionimproves the life and performance of these front-end acetylene converterreactors. These advantages are given by way of non-limiting examplesonly, and additional benefits and advantages will be readily apparent tothose skilled in the art in view of the description set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow chart illustrating an embodiment of thepresent invention for the removal of mercaptans by thioetherification.

FIG. 2 is a schematic flow chart illustrating an embodiment of thepresent invention for the removal of mercaptans by thioetherificationwherein a first catalyst is used in the form of distillation packing asa lower bed in a catalytic distillation reactor.

FIG. 3 is a schematic flow chart illustrating an embodiment of thepresent invention for the removal of mercaptans from liquefied petroleumgas feed by thioetherification.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to thioetherification processes for theremoval of mercaptans in charge gas streams. Conventional causticscrubber systems and adsorption techniques used to remove sulphur fromcharge gas streams have very low mercaptan removal capability. Thepresent invention provides for improved sulphur removal from thesestreams.

The present invention differs from conventional systems and techniquesin at least the following way. The present invention uses reactionsbetween components already in the charge gas to remove sulphur. Thethioetherification reaction removes mercaptans from the charge gasstream by converting them to less volatile compounds which may then bereadily separated from the charge gas stream by fractional distillation.In particular, the reaction joins the mercaptan to olefins, diolefins,and/or acetylenics contained in the charge gas and produces highermolecular weight thioethers. This results in the reactor product mixturecomprising high boiling point thioethers.

Thioetherification has been used for the removal of mercaptans fromrefinery streams in the past. The present invention differs from theprior art thioetherification processes in at least the following ways.The present invention can effectively remove mercaptans from feed gascompositions that comprise significantly higher olefinic and diolefiniccontent and wider molecular weight ranges, such as hydrogen gas and C₁to C₆ hydrocarbons that cannot effectively be removed by prior artprocesses. The present invention also uses a catalyst comprisingpalladium and silver as opposed to Ni-based catalysts used in the priorart processes.

In one embodiment, the present invention involves a process comprisingthe steps of (a) feeding to a reactor a gas phase mixture comprisinghydrocarbons and mercaptans to produce a reactor product mixture,wherein said reactor comprises a catalyst which is capable of catalyzingthe thioetherification of mercaptans to thioethers; (b) feeding thereactor product mixture to a distillation unit comprising an uppersection and a lower section; (c) separating lower boiling pointhydrocarbons from the thioethers wherein the lower boiling pointhydrocarbons are substantially contained in the upper section and thethioethers are substantially contained in the lower section; and (d)recovering the lower boiling point hydrocarbons from the upper section.

FIG. 1 is a schematic flow chart illustrating one embodiment of theprocess of the present invention for the removal of mercaptans bythioetherification. The feed, such as a charge gas stream, is fed (12)into the thioetherification reactor (15). The feed may comprise hydrogengas, hydrocarbons, mercaptans and mixtures thereof. The hydrocarbonstypically range from C₁ to C₆. The hydrocarbons may also compriseolefins, diolefins, acetylenic compounds and mixtures thereof. Themercaptans typically comprise light mercaptans, such asmethyl-mercaptan, ethyl-mercaptan, propyl-mercaptans andbutyl-mercaptans. Sulphur species such as H₂S may also be present.

The mercaptans may be present in the charge gas stream at concentrationsgreater than about 5 ppm. Typically, the amount of mercaptans present inthe charge gas stream is greater than about 10 ppm, and more typicallymercaptans are present in the charge gas stream at concentrations ofgreater than about 50 ppm. The mercaptan concentration may be as high as1000 ppm or more in the charge gas stream.

The reactor (15) comprises a catalyst, such as a fixed bed catalyst. Thepreferred catalyst of the present invention comprises palladium andsilver. Preferably, the amount of palladium present in the catalyst isgreater than about 100 ppm. More preferably, the amount of palladiumpresent in the catalyst is greater than about 200 ppm. Most preferably,the amount of palladium present in the catalyst is greater than about500 ppm. Preferably, the amount of silver present in the catalyst isgreater than about 50 ppm. More preferably, the amount of silver presentin the catalyst is greater than about 100 ppm. The preferred molar ratioof palladium to silver in the catalyst of the present invention rangesfrom about 0.1 to about 10. More preferably, the molar ratio ofpalladium to silver in the catalyst of the present invention ranges fromabout 0.2 to about 1. Most preferably, the molar ratio of palladium tosilver in the catalyst of the present invention ranges from about 0.2 toabout 0.5.

The reactor (15) is preferably operated at pressures, temperatures andin an atmosphere capable of catalyzing the thioetherification ofmercaptans to thioethers. The reactor (15) may also be operated atpressures, temperatures and in an atmosphere capable of hydrogenation ofunsaturated hydrocarbons, such as diolefins and acetylenics. In apreferred embodiment, the reactor is operated at a pressure of betweenabout 100 psig and 250 psig, at a temperature of about 120° F. to 250°F.

The reactor product mixture is fed (22) to a distillation unit (25)comprising an upper section (26) and a lower section (27). The reactorproduct mixture is distilled such that the lighter hydrocarbons arerecovered in the overhead (32) and the remaining compounds, includingthioethers, exit in the bottoms (42). Preferably, the distillation unitis operated at a pressure of between about 100 psig and 250 psig, at atemperature of about 100° F. to 250° F. Preferably, the overhead stream(32) has a mercaptan concentration of less than about 5 ppm. Theoverhead stream may have a mercaptan concentration of less than about 2ppm, and in some embodiments the mercaptan concentration may be lessthan about 1 ppm.

In an alternative embodiment, the present invention involves a processfor removing mercaptans comprising the steps of (a) feeding to adistillation unit a gas phase comprising hydrocarbons and mercaptans,wherein said distillation unit comprises a first catalyst which iscapable of catalyzing the thioetherification of mercaptans tothioethers, an upper section, a lower section, and a gas phase mixturefeed point, wherein the feed point is positioned between the firstcatalyst and the lower section; (b) separating lower boiling pointhydrocarbons from the thioethers wherein the lower boiling pointhydrocarbons are substantially contained in the upper section and thethioethers are substantially contained in the lower section; and (c)recovering the lower boiling point hydrocarbons from the upper section.

FIG. 2 is a schematic flow chart illustrating this alternativeembodiment of the process of the present invention wherein a firstcatalyst is used in the form of distillation packing as a lower bed in acatalytic distillation reactor. The feed, such as a charge gas stream(12), is fed into a catalytic distillation tower (45) at a feed point(14). The feed may comprise hydrogen gas, hydrocarbons, mercaptans andmixtures thereof as previously described. The catalytic distillationtower (45) comprises a thioetherification section (35) and, optionally,a second catalyst section (55). The feed point (14) is positionedbetween the thioetherification section (35) and the lower section (47)of the distillation tower. The thioetherification section preferablycomprises a Pd/Ag catalyst of the type previously described.

The optional second catalyst section (55) is preferably positionedbetween the thioetherification section (35) and the upper section (36).The second catalyst may be any desired catalyst to promote furtherreaction of the hydrocarbon components contained in the feed stream toobtain the desired products. The positioning of the thioetherificationsection (35) above the feed point (14) may be used to guard the optionalsecond catalyst section (55) located higher in the tower (45) fromfouling and deactivation from the mercaptans. Because the mercaptanswill react over the thioetherification section (35) to form heavierthioethers, the mercaptans will not act as a catalyst poison to thesections located higher in the tower.

In yet another embodiment, the present invention involves a process forremoving mercaptans comprising the steps of (a) feeding to a reactor aliquefied petroleum gas mixture comprising hydrocarbons and mercaptans,wherein said reactor comprises a catalyst which is capable of catalyzingthe thioetherification of mercaptans to thioethers; (b) supplementingthe reactor with hydrogen gas to produce a reactor product mixture; (c)feeding the reactor product mixture to a distillation unit comprising anupper section and a lower section; (d) separating lower boiling pointhydrocarbons from the thioethers wherein the lower boiling pointhydrocarbons are substantially contained in the upper section and thethioethers are substantially contained in the lower section; and (e)recovering the lower boiling point hydrocarbons from the upper section.

FIG. 3 is a schematic flow chart illustrating this embodiment of theprocess of the present invention for the removal of mercaptans fromliquefied petroleum gas by thioetherification. The feed (52), such as aliquefied petroleum gas, is fed into the thioetherification reactor(15). The feed (52) may comprise hydrogen gas, hydrocarbons, mercaptansand mixtures thereof as described previously. In a preferred embodiment,the feed is a back-end C₃-C₅ LPG. The thioetherification reactorpreferably contains a Pd/Ag catalyst of the type previously described.

In this embodiment, the thioetherification reactor (15) is supplementedwith hydrogen gas. The hydrogen gas may be supplemented in the reactorby addition of hydrogen gas (62) into the feed (52), by addition ofhydrogen gas (63) directly to the thioetherification reactor (15), or byaddition to both the feed and the reactor. Preferably, the molar ratioof hydrogen gas to the feed ranges from about 0.001 to about 0.5. Morepreferably, the molar ratio of hydrogen gas to the feed ranges fromabout 0.01 to about 0.2, and most preferably, the ratio of the amount ofhydrogen gas to the amount of feed ranges from about 0.01 to about 0.1.

The reactor (15) is preferably operated at pressures, temperatures andin an atmosphere capable of catalyzing the thioetherification ofmercaptans to thioethers. The reactor (15) may also be operated atpressures, temperatures and in an atmosphere capable of hydrogenation ofunsaturated hydrocarbons, such as diolefins and acetylenics. In apreferred embodiment, the thioetherification reactor is operated at apressure of between about 100 psig and 150 psig, at a temperature ofabout 120° F. to 250° F.

The reactor product mixture is fed (72) to a distillation unit (25)comprising an upper section (26) and a lower section (27). The reactorproduct mixture is distilled such that the lighter hydrocarbons arerecovered in the overhead (82) and the remaining compounds, includingthioethers, exit in the bottoms (92). Preferably, the distillation unitis operated at a pressure of between about 100 psig and 250 psig, at atemperature of about 120° F. to 250° F. The tower is typically operatedas a dehexanizer (i.e. pentane and lighter components in the overheadstream), which allows the C₄ and C₅ dienes and the mercaptans to passthrough the catalyst zone and the thioethers (which are C₆+ fractions)are removed with the bottoms. Preferably, the recovered overheadcompounds contains a mercaptan concentration of less than about 5 ppm.The overhead stream may have a mercaptan concentration of less thanabout 2 ppm, and in some embodiments the mercaptan concentration may beless than about 1 ppm.

One skilled in the art will recognize that numerous variations orchanges may be made to the process described above without departingfrom the scope of the present invention. Accordingly, the foregoingdescription of preferred embodiments and following examples are intendedto describe the invention in an exemplary, rather than a limiting,sense.

Applicants specifically incorporate the entire content of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

EXAMPLES Example 1

A gas phase mixture of hydrocarbons and hydrogen was passed over a fixedbed of hydrogenation catalyst at total pressure of 150 psig. The molarcomposition of the feed is given in Table 1.

TABLE 1 Component Volume (%) Hydrogen 18.200 Nitrogen 26.230 CarbonMonoxide 0.060 Ethyl-Mercaptan 0.002 Ethylene 28.554 Acetylene 0.073Propane 0.217 Propylene 17.832 n-Butane 0.037 Propadiene 0.281T-2-Butene 0.724 1-Butene 5.889 C-2-Butene 0.228 1,3-Butadiene 0.929Methylacetylene 0.399 Isoprene 0.311

Gas samples of the feed and product were collected at specified timeintervals, in sample bags and analyzed for hydrogen, hydrocarbons andsulphur compounds. An RGA GC was used to test for hydrogen and a FID GCfor hydrocarbons. The effluent streams from the laboratory adsorptionunit were also analyzed by gas chromatograph equipped with a sulphurchemiluminescence detector (SCD GC). Identification of select componentsin some samples was achieved by analyzing those samples by GC-MS.

A low Pd (140 ppmw)—low Ag (380 ppmw) catalyst formulation was used. Thetest was run at 176° F. and gas hourly space velocity (GHSV) of 3,800h⁻¹. The presence of only 20 ppm of mercaptan in the feed had asignificant impact on the catalyst activity. At 176° F. the productivityachieved with ethyl mercaptan in the feed was initially 35% of theproductivity with the sulphur free feed. A fter only 24 hrs of testing,a significant drop to less than 10% of its original activity wasobserved as a result of ethyl mercaptan deactivation. Results aresummarized in Table 2 below.

Example 2

A high Pd catalyst was used with 0.4% (i.e. 4,000 ppm) Pd and no Ag.This is a commercial catalyst designated as G68-C by Sud Chemie. Thistest was done 176° F. and a GHSV of 12,000 h⁻¹ with 20 ppm ofethyl-mercaptan. The test had to be run at a much higher space velocitysince it is a much more reactive catalyst and the exotherm had to becontrolled. The result of this test after 30 hrs was only a slightly(10%) lower productivity with the sulphur compared to the productivitywe had achieved with the sulphur free feed. This should be contrasted tothe behavior of the catalyst in Example 1, which had showed a verysignificant drop (65% loss in productivity) immediately after exposureto the ethyl mercaptan feed.

Continued exposure of the G68-C catalyst to this feed was maintained inorder to identify any longer term deactivation effects. After completing120 hours of testing, the drop in catalyst hydrogen productivity wasless than 20%. Butadiene conversion had only dropped from 95 to 90% andacetylene conversion from 99 to 97%. The deactivation became much fasterbetween 120 and 150 hrs with H₂ productivity dropping to about 10% ofthe original value. The catalyst deactivation rate was much slower (150hrs) than the Example 1 catalyst (24 hrs). No unknown sulphur compoundswere detected in the product using SCD GC analysis. The results aresummarized in Table 2 below.

Example 3

The catalyst used in this example comprised 800 ppm of Pd and 1000 ppmof Ag. The catalyst was tested for its effect on 20 ppmv ethyl-mercaptanat 176° F. and a GHSV of 3,800 h⁻¹. In contrast to the low sulphurtolerance of the Example 1 catalyst (which was essentially completelyinactive after 30 hrs of testing), the Example 3 catalyst exhibited goodacetylene hydrogenation activity even after 70 hrs of testing (60%acetylene conversion from 100% for the fresh catalyst). The butadieneand isoprene conversions were around 5%, down from 90% for the freshcatalyst. And, the MA conversion was 20% down from 90% for the freshcatalyst.

Even further along the test, after 200 hrs, this catalyst still had goodacetylene hydrogenation activity. Acetylene conversion stabilized atabout 90% (from 100% for the S-free performance) and butadiene andisoprene conversions were around 20% (down from 90% for the sulphur(S)-free performance). Results are summarized in Table 2 below.

TABLE 2 Example 1 Example 2 Example 3 GHSV 3800 12000 3800 S-Free H₂Productivity 0.005 0.07 0.008 (lbmoles/lb cat/hr) Acetylene Conversion(%) 100 100 100 Ethylene Gain/Loss (%) −4 −34 −8 BD Conversion (%) 95 9899 S-Feed H₂ Productivity 0.0017 0.05 0.005 SOR (lbmoles/lb cat/hr)Acetylene Conversion (%) 97 98 100 Ethylene Gain/Loss (%) 0 −25 −1 BDConversion (%) 40 95 97 S-Feed H₂ Productivity 0.0002 0.003 0.003 EOR(lbmoles/lb cat/hr) Acetylene Conversion (%) 12 34 90 Ethylene Gain/Loss(%) 0.1 0.0 0 BD Conversion (%) 1 17 40 Run Duration (hrs) 24 150 230

The sulphur analysis of the product showed there was a shift in thesulphur product distribution from ethyl-mercaptan to heavier sulphurspecies which was quantitative. Identification of the unknown heaviersulphur peaks, about 4 or 5 peaks, in the C₄-C₆ region in the productwas performed. Using GC-MS, the unknown compounds were identified as C₄and C) thioethers both straight chain and cyclic. The most abundantproduct was diethyl-sulfide followed by ethyl-propyl-sulfide andmethyl-tetra-hydro-thiopene. These products are a result of C₂ or C₃olefins or diolefins reaction with ethyl-mercaptan through athioetherification reaction.

The components and their distribution are provided in Table 3.

TABLE 3 Concentration Component ppmv Structure 2-methylthietane 1.8

Di-ethyl-sulfide 6.0 CH₃—CH₂—S—CH₂—CH₃ Ethyl-isopropyl 2.2CH₃—CH₂—S—CH₂—CH₂—CH₃ sulfide Ethyl-n-propyl 2.4 CH₃—CH₂—S—CH—(CH₃)₂sulfide Methyl tetra- hydro-thiophenes 5.0

Diethyl-disulfide 2.0 CH₃—CH₂—S—S—CH₂—CH₃ Total 19.4

The most abundant product was diethyl-sulfide followed byethyl-propyl-sulfides and methyl-tetra-hydro-thiophene. These productsare potentially a result of unsaturated C₂ or C₃ compounds withethyl-mercaptan through a thioetherification reaction. The presence ofdiethyl-sulfide in particular is an indication that a C₂ hydrocarboneither acetylene or ethylene, very much in abundance in the feed, arecontributing to the reaction with the mercaptan. Based on these resultsa combination of Ag and Pd can catalyze these reactions, preferably whenboth metals are present in sufficiently high enough concentrations(>about 800 ppm).

1. A process for removing mercaptans from a gas phase mixture,comprising the steps of. (a) feeding to a reactor a gas phase mixturecomprising hydrocarbons and mercaptans, wherein the reactor comprises acatalyst which is capable of catalyzing the thioetherification ofmercaptans to thioethers to produce a reactor product mixture; (b)feeding the reactor product mixture to a distillation unit comprising anupper section and a lower section; (c) separating lower boiling pointhydrocarbons from the thioethers wherein the lower boiling pointhydrocarbons are substantially contained in the upper section and thethioethers are substantially contained in the lower section; and (d)recovering the lower boiling point hydrocarbons from the upper section.2. The process of claim 1, wherein the catalyst comprises greater than100 ppm by weight palladium and greater than 50 ppm by weight silver. 3.The process of claim 1, wherein the catalyst comprises greater than 500ppm by weight palladium and greater than 100 ppm by weight silver. 4.The process of claim 2, wherein the molar ratio of palladium to silveris between 0.1 to
 10. 5. The process of claim 2, wherein the molar ratioof palladium to silver is between 0.2 to 0.5.
 6. The process of claim 1,wherein the reactor is operated at a pressure of between 100 psig to 250psig and a temperature of 120° F. to 250° F.
 7. A process for removingmercaptans from a gas phase mixture, comprising the steps of: (a)feeding to a distillation unit a gas phase comprising hydrocarbons andmercaptans, wherein the distillation unit comprises (i) a first catalystwhich is capable of catalyzing the thioetherification of mercaptans tothioethers, (ii) an upper section; (iii) a lower section, and (iv) a gasphase mixture feed point, wherein the feed point is positioned betweenthe first catalyst and the lower section, (b) separating lower boilingpoint hydrocarbons from the thioethers wherein the lower boiling pointhydrocarbons are substantially contained in the upper section and thethioethers are substantially contained in the lower section; and (c)recovering the lower boiling point hydrocarbons from the upper section.8. The process of claim 7, wherein the catalyst comprises greater than100 ppm by weight palladium and greater than 50 ppm by weight silver. 9.The process of claim 7, wherein the catalyst comprises greater than 500ppm by weight palladium and greater than 100 ppm by weight silver. 10.The process of claim 8, wherein the molar ratio of palladium to silveris between 0.1 to
 10. 11. The process of claim 8, wherein the molarratio of palladium to silver is between 0.2 to 0.5.
 12. The process ofclaim 7, wherein the reactor is operated at a pressure of between 100psig to 250 psig and a temperature of 120° F. to 250° F.
 13. A processfor removing mercaptans from a gas phase mixture, comprising the stepsof: (a) feeding to a reactor hydrogen gas and a liquefied petroleum gasmixture comprising hydrocarbons and mercaptans to produce a reactorproduct mixture, wherein the reactor comprises a catalyst which iscapable of catalyzing the thioetherification of mercaptans tothioethers; (b) feeding the reactor product mixture to a distillationunit, wherein the distillation unit comprises an upper section and alower section; (c) separating lower boiling point hydrocarbons from thethioethers wherein the lower boiling point hydrocarbons aresubstantially contained in the upper section and the thioethers aresubstantially contained in the lower section; and (d) recovering thelower boiling point hydrocarbons from the upper section.
 14. The processof claim 13, wherein the catalyst comprises greater than 100 ppm byweight palladium and greater than 50 ppm by weight silver.
 15. Theprocess of claim 13, wherein the catalyst comprises greater than 500 ppmby weight palladium and greater than 100 ppm by weight silver.
 16. Theprocess of claim 14, wherein the molar ratio of palladium to silver isbetween 0.1 to
 10. 17. The process of claim 14, wherein the molar ratioof palladium to silver is between 0.2 to 0.5.
 18. The process of claim13, wherein the reactor is operated at a pressure of between 100 psig to250 psig and a temperature of 120° F. to 250° F.
 19. The process ofclaim 8 wherein the distillation column further comprises a secondcatalyst wherein the second catalyst is positioned between the firstcatalyst and the upper section.
 20. The process of claim 13 wherein thehydrogen gas is mixed with the liquefied petroleum gas mixture prior tobeing fed to the reactor.